Sorry to comment this late, but that Dell monitor is a truly great monitor.

However, instead of hooking up multiple monitors to a single PC, I would recommend running multiple computers with a single monitor each. Using InputDirector makes the system behave exactly like if they were all on same same PC, but everything runs much faster. Imho, multiple medium-spec computers run multiboxing better than a single uber-spec PC - and you still control everything exactly the same way.

Crossfire/SLI should in theory work great with multiboxing, but I don't know. Could be issues with the driver or game that causes issues, decreasing the theoretical performance improvement (that's very often the case though - crossfire/SLI is a pretty horrible technical solution imho). I have seen a lot of complaints from AMD/Crossfire users on the Rift forums about performance problems.